Communication system with signal converter between networks

ABSTRACT

An information transmission system with a first user network in which pulse code modulation is used, with transition points connecting the networks. There are also signal preparation and data format adaptation devices in the terminals and in the transition point there is a source network recognition device by which a source network identification symbol is added to the call number from the other user network.

BACKGROUND OF THE INVENTION

The invention relates to a communication system according to thepreamble of patent claim 1, and also to interfaces matched thereto.

A system of this type is known from German Offenlegungsschrift3,033,871. This communication system consists of a first subscribernetwork in which the voice processing is executed with pulse codemodulation and of a second subscriber network in which the voiceprocessing is executed with delta modulation. The subscribers of thenetworks are connected to one another across an interface, with asignaling converter being provided in the interface. The subscriberterminals of the first network, which are equipped with acryptogenerator, additionally have a delta modulation devicecorresponding to the second network for voice processing.

SUMMARY OF THE INVENTION

The object of the invention is to disclose a communication system orinterfaces of the type mentioned at the beginning in which it ispossible to connect networks having different bit rates in a simplemanner.

This object is achieved according to the invention by a communicationsystem, having a first subscriber network in which the subscriberterminals have a voice processing device employing pulse codemodulation, having at least one further subscriber network in which thesubscriber terminals have voice processing devices and in which the bittransmission rate is not greater than that in the first subscribernetwork, having at least one interface with signaling converterconnecting the networks, having predetermined subscriber terminals ofthe first subscriber network, which additionally have a voice processingdevice in accordance with each of the further subscriber networks. Thesubscriber terminals have data format adaptation devices connecteddownstream of the additional voice processing devices. The interfaceshave data format adaptation devices, and each of the interfaces has asource network identification device with which a source networkidentifier is appended to the call number from the further subscribernetwork, by means of which one of the additional voice processing anddata format adaptation devices is switched on in the subscriber terminalof the first network. One of the interfaces has a data format adaptationdevice and a source network identification device, with which a sourcenetwork identifier is appended to the call number from a furthernetwork, by means of which one of the additional voice processing anddata format adaptation devices is switched on in the subscriber terminalof the first network. Another of the interfaces has a data formatadaptation device and a modem for digital signal transmission in ananalog network. A source network identification device is provided, withwhich a source network identifier is appended to the call number fromthe analog network, by means of which one of the additional voiceprocessing and data format adaptation devices is switched on in thesubscriber terminal of the first network.

A great advantage of the communication system according to the inventionis that it is also possible to exchange encrypted messages betweensubscribers on different networks without the message appearing in theinterface without encryption.

A further advantage is conferred by the fact that it is not necessary toalter the existing networks in the communication system according to theinvention.

Likewise it is not necessary to alter any of the subscriber terminals inthe corresponding networks (Eurocom network and IVSN Nato network).

An extension of the communication system according to the invention tofurther digital or analog networks is readily possible.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention which are believed to be novel,are set forth with particularity in the appended claims. The invention,together with further objects and advantages, may best be understood byreference to the following description taken in conjunction with theaccompanying drawings, in the several Figures in which like referencenumerals identify like elements, and in which:

FIG. 1 shows a communication system consisting of three subscribernetworks,

FIG. 2 shows the subscriber terminal according to the invention,

FIG. 3 shows a flowchart for explaining how the subscriber terminalfunctions,

FIG. 4 shows the interface according to the invention between PCM anddelta-modulated network,

FIG. 5 shows the transition point according to the invention between PCMand analog network, and

FIG. 6 shows a pulse diagram for explaining the transmission method inthe PCM network.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates three subscriber networks:

A first network N1, a so-called ISDN network, in which the data aretransmitted at a bit rate of 64 kbits per second. For voice processing,that is to say for digitizing the analog voice signal or, in theopposite direction, for converting the incoming digital voice signalinto an analog signal, pulse code modulation is employed in thesubscriber terminals Tn11, 12, . . . .

A second network N2, a so-called Eurocom network, in which the data aretransmitted at a bit rate of 16 kbits per second. Delta modulation isemployed for voice processing in the subscriber terminals Tn21, 22.

A third network N3, a so-called IVSN Nato network. This is an analognetwork in which the voice signal is transmitted as an analog signalbetween the subscriber terminals Tn31, 32. If so-called vocoders areemployed for voice processing in the subscriber terminals Tn31, 32, thedigital voice signal is transmitted at a transmission rate of 2.4 kbitsper second instead of the analog voice signal.

In all of the networks N1, N2, N3, the digital voice signals arenormally transmitted without encryption, but they are also transmittedencrypted if cryptogenerators are employed in selected subscriberterminals.

Two interfaces U1, U2 are used to connect the networks N1 to N3. Thefirst interface U1 is connected between the first N1 and the secondnetwork N2, and the second interface U2 is connected between the firstnetwork N1 and the third network N3. The interfaces U1 and U2 areexplained more fully later with reference to FIGS. 4 and 5.

A subscriber terminal Tn1 for an ISDN network (first network N1) isillustrated in FIG. 2. It has here a voice processor 1 employing pulsecode modulation, a subscriber line device 2 for the ISDN format, and aline terminating device 3 in accordance with the ISDN transmissionprotocol. In addition, the subscriber terminal Tn1 contains acryptogenerator 4 for encrypting the digital voice signal.

According to the invention, the subscriber terminal Tn1 has additionaldevices matched to the second network (N2) (Eurocom network). These area voice processing device 8 employing delta modulation (16 kbit/sec), asubscriber line device 9 in accordance with the Eurocom format, and alsoa data format adaptation device 10 for converting the voice signaldigitized according to the Eurocom format into a voice signal digitizedaccording to the ISDN protocol.

According to the invention, the subscriber terminal Tn1 has furtheradditional devices matched to the third network N3 (IVSN Nato network).These are an LPC vocoder 5 (2.4 kbit/sec) for voice processing, asubscriber line device 6 for matching to the IVSN format, and also adata format adaptation device 7 for converting the voice signaldigitized according to the IVSN protocol into a voice signal digitizedaccording to the ISDN protocol.

The analog voice signal is thus digitized with three different methodsin the subscriber terminal Tn1 and output to the first network N1. Theone of the voice processing devices 1, 5, 8 corresponding to the networkwhere the called subscriber is located is always switched on here.Likewise, each of the voice signals can be encrypted using thecryptogenerator 4. The bit rate of the cryptogenerator 4 is matched tothe bit rate of the voice processing device 1, 5, 8 that is switched onand is connected directly downstream of the voice digitizer (deltamodulator 8, LPC vocoder 5) with associated subscriber line device 6, 9.

Such a connection establishment is described below with reference toFIG. 3.

To start with, the receiver is usually lifted and a number is dialled toestablish a connection between one subscriber in the first network N1and the called subscriber. This dialling also entails a network exit inthe case of a subscriber located outside the network.

If the dialling does not entail a network exit (network exit n), thevoice processing device 2 employing pulse code modulation is switchedon, the cryptogenerator 4 may be connected if desired, and theconversation between the two subscribers takes place.

If the dialling does entail a network exit (network exit y), in one casethe connection is established to the second network N2 (Eurocom network)to the subscriber there (Eurocom y) via the transition point U1. Thevoice processing device 8 employing delta modulation is switched on inthe subscriber terminal Tn1, the cryptogenerator 4 (matched to 16kbit/sec) may be connected if desired, and the Eurocom/ISDN formatadaptation device 10 is activated. If the dialling entails a networkexit (via the second interface U2) to the third network N3 (Eurocom n),then the LPC vocoder 5 is switched on in the subscriber terminal Tn1 forvoice processing, if necessary the cryptogenerator 4 (matched to 2.4kbit/sec) is connected, and the IVSN/ISDN format adaptation device isactivated.

According to the invention, therefore, quite normal voice signals(non-encrypted or encrypted text) digitized and formatted in accordancewith the ISDN network are transmitted in the first network N1. Moreover,so-called pseudo-ISDN messages are also transmitted in this ISDNnetwork. These are the analog voice signals processed with a vocoder orin accordance with the delta modulation method, which were convertedusing the data adaptation devices 7, 10 into the ISDN format and aretransmitted in the first network 1 like normal ISDN signals.

The establishment of the connection between a calling subscriber in oneof the networks N2, N3 and a called subscriber in the first network N1will be discussed later.

The interface U1 is illustrated as a block circuit diagram in FIG. 4. Onthe side facing the first network N1 it contains a line terminatingdevice 11 in accordance with the ISDN format, and on the side facing thesecond network N2 it contains a line terminating device 12 in accordancewith the Eurocom format. According to the invention, a data formatadaptation device 13 for converting these two data formats and asignaling converter 14 for converting the signaling data (call number,busy and free tones, etc.) are connected in between.

Furthermore, a source network identification device 15 is provided inthe interface U1. In this source network identification device 15, inthe event of signaling from the second network N2, a source networkidentifier is appended to the normal call number (the called subscriberis located in this case in the first network N1). By means of thissource network identifier, the voice processing and formatting path (8,9, 10) corresponding to the second network N2 is switched on in thesubscriber terminal Tn1 of the called subscriber.

FIG. 5 illustrates the second interface U2. On the side facing the firstnetwork N1 it contains a line terminating device 21 in accordance withthe ISDN format, and on the side facing the analog third network N3 itcontains a line terminating device 22 in accordance with the IVSNformat.

A PCM codec 23 (coder-decoder) is connected between these two lineterminating devices 21, 22 for unencrypted voice transmission. Analogvoice signals from the third network N3 are digitized in the PCM codec23 with the pulse code modulation method, and digital voice signals fromthe first network N1 are converted into the analog voice signal.

As already explained with reference to FIG. 1, it is also possible totransmit digital voice signals, in particular encrypted digital voicesignals, in the analog network N3. For this purpose, according to theinvention a data format adaptation device 24, a signaling converter 25,and downstream of these last two a modem 27 are inserted between the twoline terminating devices 21, 22. In this arrangement, the digital voicesignals of the first network N1 and of the third network N3 areconverted in the data format adaptation device 24 together with themodem 27. The signaling converter 25 likewise serves together with themodem 27 to convert the signaling used in the first network N1 and inthe third network N3.

Moreover, a source network identification device 26 is also providedhere, by means of which a source network identifier is appended in thecase of a call from the third network N3 (the called subscriber islocated in the first network N1) to this call number. As a result ofthis source network identifier, the voice processing and formatting path(5, 6, 7) corresponding to the third network N3 is connected in thesubscriber terminal.

It is described with reference to FIG. 6 how a delta-modulated voicesignal is converted into a PCM-modulated voice signal in the data formatadaptation device 7 of the subscriber terminal Tn1, FIG. 2 (or in thedata formatting device 13 in the interface U1, FIG. 4), and convertedback from this into a delta-modulated voice signal. For this purpose,the delta-modulated voice signal is sampled with the PCM sampling clock,and a so-called pseudo-PCM signal is formed. In the line terminatingdevice 3 of the subscriber terminal Tn1 (or in the line terminatingdevice 11 in the interface U1, FIG. 4), this pseudo-PCM signal ishandled and formatted exactly like a conventional PCM voice signal.

In the data format adaptation device 13 of the interface U1, FIG. 4 (orin the data format adaptation device 7 of the subscriber terminal Tn1,FIG. 2), this pseudo-PCM signal is sampled with the sampling clockcorresponding to the delta modulation method, and the delta-modulatedsignal is recovered, as can be seen in the drawing, with a time offset.This delta-modulated signal is then output to the second network N2 (orto the subscriber line device 6, FIG. 2) via the line terminating device12.

The same procedure--conversion of the delta modulated signal into apseudo-PCM signal and the recovery of the delta-modulated signal--isexecuted in the data format adaptation device 13 of the interface U1when the digital voice signal is forwarded from the second network N2into the first network N1.

The conversions in the second interface U2, or in the signal processingpath of the subscriber terminal corresponding to the third network N3,are executed analogously.

The invention is not limited to the particular details of the apparatusdepicted and other modifications and applications are contemplated.Certain other changes may be made in the above described apparatuswithout departing from the true spirit and scope of the invention hereininvolved. It is intended, therefore, that the subject matter in theabove depiction shall be interpreted as illustrative and not in alimiting sense.

What is claimed is:
 1. A communication system comprising: a firstsubscriber network in which subscriber terminals have a voice processingdevice employing pulse code modulation; at least one further subscribernetwork in which subscriber terminals have voice processing devices andin which a bit transmission rate is not greater than a bit transmissionrate in the first subscriber network; at least one interface withsignaling converter connecting the networks; predetermined subscriberterminals of the first subscriber network having at least one additionalvoice processing device in accordance with the at least one furthersubscriber network; the predetermined subscriber terminals having dataformat adaptation devices connected downstream of the additional voiceprocessing devices; each of the interfaces having data format adaptationdevices; each of the interfaces having a source network identificationdevice with which a source network identifier is appended to a callnumber from the further subscriber network, by means of which one of theadditional voice processing and data format adaptation devices isswitched on in the respective predetermined subscriber terminal of thefirst network.
 2. The communication system according to claim 1, whereinthe voice processing device of one of the further subscriber networkshas a means for delta modulation.
 3. The communication system accordingto claim 1, wherein the further network is an analog network, whereinthe subscriber terminals of the first network additionally have avocoder that can be switched on for voice digitization and a data formatadaptation device, at least one of the subscriber terminals in theanalog network having a vocoder that can be switched on, wherein theinterface has a modem, a data format adaptation device and a sourcenetwork identifier is appended to the call number from the analogsubscriber network, by means of which the additional voice processingand data format adaptation device is switched on in the subscriberterminal of the first network.
 4. The communication system according toclaim 1, wherein predetermined subscriber terminals of each of theconnected subscriber networks have a cryptogenerator, wherein thecryptogenerator in the subscriber terminals of the first network has avariable bit rate that can be matched to different bit rates of thevoice processing devices and is connected directly downstream thereof.5. The communication system according to claim 1, wherein the interfacehas a data format adaptation device and a source network identificationdevice, with which a source network identifier is appended to a callnumber from the further subscriber network, by means of which one of theadditional voice processing and data format adaptation devices isswitched on in the subscriber terminal of the first network.
 6. Thecommunication system according to claim 1, wherein the interface has adata format adaptation device and a modem for digital signaltransmission in an analog network and a source network identificationdevice, with which a source network identifier is appended to a callnumber from the analog network, by means of which one of the additionalvoice processing and data format adaptation devices is switched on inthe subscriber terminal of the first network.
 7. The communicationsystem according to claim 6, wherein the interface has a PCM codec fordigitizing analog signals and for converting digital signals into analogsignals.